The invention relates to digital imaging. More specifically, the invention relates to optical scanners and methods of increasing scanner resolution.
Scanners are typically advertised as having two resolutions: a hardware resolution and an enhanced or interpolated resolution. The hardware resolution provides a measure of the imaging ability of the scanner. A typical resolution for a low-end scanner might be 300 dots per inch (xe2x80x9cdpixe2x80x9d).
The hardware resolution of a scanner is dependent, in part, upon quality of the scanner""s sensor array and imaging optics. Ideally, the sensor array and optics would image a point source as a point of light. In reality, however, the image is smeared. Factors contributing to the smearing of the image include the geometry of the sensor""s receptive field, optical defocus and chromatic aberration effects in which different wavelengths of light from the single point source do not coincide on the sensor array""s surface. Scanners including higher quality sensor arrays and imaging optics will cause less smearing than scanners including lower quality sensor arrays and imaging optics.
The enhanced or interpolated resolution, in contrast, is more a function of software. Software-based techniques such as bilinear interpolation and pixel replication are typically used to enhance the hardware resolution. For example, a hardware resolution of 300 dpi might be enhanced to a resolution of 4800 dpi. Enhancing or interpolating the hardware resolution allows the size of the scanned image to be enlarged.
However, enhancing the hardware resolution does not increase the real detail that is collected by the scanner. That is, enhancing the hardware resolution does not provide real information about the image. An exemplary bilinear interpolation algorithm might interpolate a pixel by finding four neighboring pixels, multiplying color intensities of the four neighboring pixels by weighting coefficients, and adding the results to obtain the color intensity value of the interpolated pixel. Thus, resolution enhancement is merely estimated from the information provided by the scanner, it does not increase the amount of real information obtained by the scanner.
Hardware resolution of the scanner may be increased by increasing the number of detector elements in the sensor array, using higher quality imaging optics, etc. For instance, the density of detector elements could be increased from 300 dpi to 600 dpi, or aspherical imaging lenses could be used instead of spherical imaging lenses.
However, increasing the number of detector elements and improving the quality of the imaging optics will substantially increase the cost of manufacturing the scanner. The market for scanners is fiercely competitive. Increasing hardware resolution by increasing the density of detector elements or improving the quality of the optics is something that manufacturers of low-end scanners cannot afford.
There is a need to increase the hardware resolution of a scanner without substantially increasing the cost of manufacturing the scanner.
The present invention offers an approach for increasing scanner resolution without substantially increasing the cost of manufacture. A first representation of an image is generated during a first scan of the image is performed, and a second representation of the image is generated during a second scan of the image. A motion error is intentionally induced in one of the scans. Using a super resolution technique, the first and second representations are processed to generate a third representation of the image. The third representation of the image has a higher resolution than either then first representation or the second representation.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.